LINEAR LTM4627 User Guide

15A µModule Regulator Solves Thermal Problems by Converting 12V to 1V with High Efficiency Eddie Beville

Advances in silicon process technology continue system temperature, thus compromis- ing system performance and reliability.

to reduce transistor geometries down to historical levels in microprocessors, FPGAs and ASICs. The One possible solution is to use a power

power supply voltage levels necessary to power these converter module that can deliver signifi- large, complex digital devices also continue to shrink, cantly higher output power than necessary for the application, and run it at an output

creating unique power supply design challenges.

current point that maximizes efficiency.

power MOSFETs and inductors to improve

One major concern is the power regula- Of course, overly large solutions are not

low voltage conversion efficiency not

tor’s conversion efficiency at low output feasible in space-constrained systems

just an increase the solution size.

voltages. For example a typical high and the current limit of this solution is efficiency switching regulator that con- much higher than the required current.

In reality, many feature-laden digital

verts 12V to 3.3V at 15A has a conver-

devices have current requirements in the

Another solution is to use a discrete

sion efficiency of ~93%. For practical

>30A range for the low voltage sup-

power converter that is optimized for low

purposes, such a regulator incurs most

ply. Thus a 76% efficiency 1V output

output voltage efficiency. But again space

of its efficiency loss due to I2R losses.

would incur a 9.48W loss for a 30A load,

constraints and component sourcing can

Therefore 93% efficiency for processing EF FI CI EN CY

which would certainly cause thermal

be challenging. Another challenge with a

49.5W to the load equates to a 3.72W loss.

challenges. The thermal problems mul-

discrete design is how to effectively cool it

tiply with the number of 30A regula-

Likewise, a low output voltage require- and heat sink the various discrete power

tors required on a system board.

ment of 1V at 15A with an efficiency components, which have different heights.

of 76% incurs a power loss of 4.74W.

Unchecked regulator power losses, µMODULE SOLUTION

Typical high density power solutions

when added to other system power Figure 1 shows a complete 1.0V at 15A con-

are challenged to achieve high efficien-

losses create serious thermal chal- verter that uses the LTM4627 µModule

cies at low output voltages due to the

lenges. One issue is that small-geometry regulator housed in a 15mm × 15mm

size constraints of the power stage. The

ASIC or FPGA leakage currents rise with × 4.32mm package. The LTM4627 inte-

power stage must have high performance

grates the high performance power path

Figure 1. A complete 1V at 15A converter requires only a few components around the LTM4627 µModule Figure 2. Efficiency of the regulator in Figure 1 regulator, which comes in a thermally enhanced 15mm × 15mm × 4.32mm package

VOUT = 1V

f SW = 400k Hz

4.5V TO 16V

VIN EXTVCC INTVCC PGOOD

×3 VOUT

RUN VOUT 1V COUT1 COUT2 15A

f SET VOUT_LCL

470µF 100µF COMP LTM4627 DIFF_OUT 6.3V 6.3V

TRACK/SS VOSNS 82p F

MODE_PLLIN VOSNS

VIN = 5V

0.1µF VFB

VIN = 8V

SGND PGND RFB

VIN = 12V

ILOAD (A)

38 | October 2011 : LT Journal of Analog Innovation